Combined effects of tree canopy composition, landscape location, and growing season on Nothofagus forest seeding patterns in Southern Patagonia

Abstract

The ecological mechanisms that regulate seeding processes in temperate forests are poorly understood especially in the Southern Hemisphere. We studied the effect of different growing season metrics determined by the Normalized Difference Vegetation Index (NDVI) across eight annual periods between 2012 and 2020. We analyzed the seed production and biomass of two Nothofagus species in Tierra del Fuego (Argentina) to develop new tools for ecological forest management strategies. We focused on three forest types in coast and mountain landscapes: (i) pure deciduous N. pumilio, (ii) pure evergreen N. betuloides, and (iii) mixed forests with a similar proportion of both species. We performed generalized linear models for each species to analyze the influence of the growing season metrics and regional climate patterns (temperature and rainfall) considering forest types on coasts and mountains as main factors and analyzing seed production and biomass. Seed production and biomass annually varied with tree species growing at different landscape locations, with marked synchrony for each forest type, but not between different species or landscape locations (e.g. deciduous and evergreen species presented different synchrony among years). Seed production and biomass were higher when NDVI-peak was high in N. pumilio and when the growing season end was late in N. betuloides. For N. pumilio, the seed production and biomass were significantly leaded by growing season minimum temperature and growing season rainfall in coastal and mountain forests. For N. betuloides, the higher seed production and biomass were significantly influenced by non-growing season maximum temperature, growing season rainfall and non-growing season rainfall in coastal and mountain forests. These outputs highlight the importance of considering the fluctuation of the growing season in the modeling of seed production and biomass. Forest management guidelines should forecast rainy years that may benefit seedling recruitment after stand management or conservation efforts of target species (e.g. simulations of population dynamics at stand-level, decisions about passive vs active restoration in degraded forests for recover of the natural ecosystem functions).